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Statistics: The Null and Alternate Hypotheses

A Student Academic Learning Services Guide

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This document last updated: 7/27/2011

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The Null and Alternate Hypotheses: before we begin

The Null and Alternate Hypothesis statements are important parts of the analytical methods collectively known as inferential statistics

Inferential statistics are methods used to determine something about a population, based on the observation of a sample1

Information about a population will be presented in one of two forms, as a mean (?) or as a proportion (p)

Use the population mean (?) in the hypothesis statements when the question gives you information about the population in the form of an average

o e.g. "the average travel time was 40 minutes...", ? = 40 minutes

Use the population proportion (p) in the hypothesis statements when the question gives you information about the population in the form of a fraction, percentage, or decimal

o e.g. " 4 out of 5 dentists agree...", p = or p = 80% or p = .80

The Null Hypothesis: H0

Stating the Null Hypothesis is the starting point of any hypothesis testing question solution

When solving a problem, it is written as "H0:" The Null Hypothesis is the stated or assumed value of a population parameter (the

mean or proportion that is being analyzed)

o What the question says the population is doing o The current or reported condition

The necessary information tends to be in the first sentence of the problem When trying to identify the population parameter needed for your solution, look for the

following phrases:

o "It is known that..." o "Previous research shows..." o "The company claims that..." o "A survey showed that..."

When writing the Null Hypothesis, make sure it includes an "=" symbol. It may look like one of the following:

o e.g. H0: ? = 40 minutes o e.g. H0: ? 40 minutes o e.g. H0: ? 40 minutes

1 Basic statistics for business & economics, Douglas A. Lind...[et al.]. ? 3rd Canadian Ed., McGraw-Hill Ryerson, Toronto.

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The Alternate Hypothesis: H1

The Alternate Hypothesis accompanies the Null Hypothesis as the starting point to answering hypothesis testing questions

When solving a problem, it is written as "H1:" The Alternate Hypothesis is the stated or assumed value of a population parameter if the

Null Hypothesis (H0) is rejected (through testing) The necessary information tends to be found in the last sentence of the problem (or the

sentence ending in a "?") When trying to identify the information needed for your Alternate Hypothesis

statement, look for the following phrases:

o "Is it reasonable to conclude..." o "Is there enough evidence to substantiate..." o "Does the evidence suggest..." o "Has there been a significant..."

There are three possible symbols to use in the Alternate Hypotheses, depending on the wording of the question

Use "" when the question uses words/phrases such as:

o "is there a difference...?" o "is there a change...?"

Use "" when the question uses words/phrases such as:

o "is there a increase...?" o "is there more...?"

When writing the Alternate Hypothesis, make sure it never includes an "=" symbol. It should look similar to one of the following:

o e.g. H1: ? < 40 minutes o e.g. H1: ? > 40 minutes o e.g. H1: ? 40 minutes

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Student Services Building (SSB), Room 204 905.721.2000 ext. 2491

This document last updated: 7/27/2011

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Reading the Question

Here is an example problem to demonstrate the process of creating Null and Alternate Hypothesis statements.

Example

A recent survey of college campuses across Ontario claims that students spend an average of 2.7 hours a day using their cell phones. A random sample of 35 Durham College students showed an average use of 2.9 hours a day, with a standard deviation of 0.4 hours. Do Durham College students use their cell phones more than the typical Ontario college student?

Step 1: Find the population information Read the question carefully and try and find information that is being presented as, or claims to be, fact.

In the first sentence we see the phrases "A recent survey..." and "claims that..." (both are good indicators that the information we need is in that sentence)

Next, determine if you are working with a population average (?) or population proportion (p)

The information is given to us in the form of an average (2.7 hours) so we know we will use ? in the Null and Alternate Hypothesis statements

So far the Null and Alternate Hypothesis statements look like this:

H0: ? 2.7 hours H1: ? 2.7 hours

Step 2: Determine the operators (math symbols)

Read the question carefully and find the sentence that ends in "?". It is often (but not always) the last sentence of the problem

Examine the wording of the question sentence, looking for words/phrases that indicate which operator to use

The example question asks, "Do Durham College students use their cell phones more than the typical Ontario college student?"

Because the phrase "more than" is used in the question, we will use the greater than symbol (>)

The Null and Alternate Hypothesis statements now look like this:

H0: ? 2.7 hours H1: ? > 2.7 hours

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The Null and Alternate Hypothesis statements must oppose each other

So if the Alternate Hypothesis uses the greater than symbol (>), the Null Hypothesis statement must use the less than symbol ( 2.7 hours

Problem Types

During your course you will be asked to analyze and solve a variety of different hypothesis testing questions. Listed below are some of the problem types you may encounter, and what the Null and Alternate Hypothesis statements might look like.

One Sample

A comparison of sample data to the stated population information to determine if the stated population information is still true

Use the population symbols in your hypothesis statements (? and p)

o e.g. H0: ? = 40 hours H1: ? 40 hours

o e.g. H0: p = .20 H1: p .20

Two Samples

A comparison of data from one sample to data from a different sample to determine if the two populations they came from are the same

Use the population symbols in your hypothesis statements (? and p)

When comparing multiple samples, the Null and Alternate Hypothesis statements can be written two ways. Be sure to check with your instructor as to which is preferred

o e.g. H0: ? A = ? B

or

H1: ? A ? B

H0: ? A - ? B = 0 H1: ? A - ? B 0

o e.g. H0: pA = pB

or

H1: pA pB

H0: pA - pB = 0 H1: pA - pB 0

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More than Two Samples (ANOVA)

A comparison of sample data across more than two samples or "treatments" to determine if the populations are the same

When performing an ANOVA, you may be asked to comment on the variation/variance of the samples or the means of the samples. Be sure to look for the following statements to determine what symbols to use in your hypothesis statements

When..."Is there (more/less/difference) variation..."

o Use the population variance symbol (2) in the hypothesis statements

o e.g. H0: 2A = 2B

or

H1: 2A 2B

or

H0: 2A - 2B = 0 H1: 2A - 2B 0

When..."Is there difference in the mean/average..."

o Use the population mean symbol (?) in the hypothesis statements

o e.g. H0: ? A = ? B = ? C H1: the means are not equal

Linear Regression

An analysis of the relationship between two variables within a sample to determine the affect changing one of them (the independent variable) has on the other (dependent variable)

The Null and Alternate Hypothesis statements use the population correlation coefficient () instead of the population mean, proportion, or variance

o Note that this symbol is called "rho" (sounds like "row"). Although it looks like the letter "p" it is not, and has a very different meaning

o e.g. H0: = 0 H1: 0

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Multiple Regression

An analysis of the relationship between multiple variables within a sample to determine the relationship (strength and nature) of those variables. In multiple regression there is a single dependent variable, but multiple independent variables

There are usually more than one set of hypothesis statements needed to complete the problem when performing a multiple regression analysis

The first set is used when performing a "global test" to see if there is a relationship between any of the independent variables and the dependent variable.

The Null and Alternate Hypothesis statements use the symbol to represent the net regression coefficients in the population. There is a for each independent variable in the problem

o e.g. H0: 1= 2= 3 = 0

H1: not all are 0

Later in a problem you may be asked to test each independent variable's regression coefficient on its own. In this case, you will create Null and Alternate Hypothesis statements for each independent variable

o e.g. H0: 1 = 0 H1: 1 0

H0: 2 = 0 H1: 2 0

H0: 3 = 0 H1: 3 0

Chi-Squared (2)

A comparison to observed data to expected data

Symbols are not used in the Null and Alternate Hypothesis statements

o e.g. H0: there is NO difference between the (observed frequency) and the (expected frequency) H1: there IS a difference between the (observed frequency) and the (expected frequency)

durhamcollege.ca/sals

Student Services Building (SSB), Room 204 905.721.2000 ext. 2491

This document last updated: 7/27/2011

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